Embryonic Development Week 1-3

Embryonic Development

Week 1: Fertilization and Cleavage

• Fertilization: fusion of sperm and egg to form a zygote
• Cleavage: series of rapid cell divisions without significant growth
• Morula: stage at which cells begin to compact and form a solid ball
• Blastula: stage at which a fluid-filled cavity (blastocoel) forms

Week 2-3: Gastrulation

• Gastrulation: process of forming three primary germ layers
  • Ectoderm: outer layer, gives rise to skin, nervous system, and sensory organs
  • Mesoderm: middle layer, gives rise to muscles, bones, and connective tissue
  • Endoderm: inner layer, gives rise to lining of digestive system and respiratory system
• Gastrula: stage at which germ layers are established

Week 4-8: Organogenesis

• Organogenesis: process of forming organs from germ layers
• Neurulation: formation of neural tube, which gives rise to central nervous system
• Somitogenesis: formation of somites, which give rise to muscles, bones, and connective tissue
• Morphogenesis: shaping of tissues and organs

Embryonic Period (Week 3-8)

• Critical period of development, during which major organs and body systems form
• High susceptibility to teratogens, which can cause birth defects

Fetal Period (Week 9-Birth)

• Growth and maturation of organs and body systems
• Development of sensory organs and neural connections

Embryonic Stem Cells

• Totipotent: able to give rise to all cells in the body
• Pluripotent: able to give rise to all cells in the body, except for extra-embryonic tissues
• Multipotent: able to give rise to multiple cell types within a specific lineage
• Adult stem cells: multipotent cells found in adult tissues, able to differentiate into specific cell types

Embryonic Development

Week 1: Fertilization and Cleavage

• Fusion of sperm and egg forms a zygote through fertilization
• Series of rapid cell divisions without significant growth occurs during cleavage
• Morula stage: cells compact and form a solid ball
• Blastula stage: fluid-filled cavity (blastocoel) forms

Week 2-3: Gastrulation

• Gastrulation forms three primary germ layers: ectoderm, mesoderm, and endoderm
• Ectoderm gives rise to skin, nervous system, and sensory organs
• Mesoderm gives rise to muscles, bones, and connective tissue
• Endoderm gives rise to lining of digestive system and respiratory system
• Gastrula stage: germ layers are established

Week 4-8: Organogenesis

• Organogenesis forms organs from germ layers
• Neurulation forms neural tube, which gives rise to central nervous system
• Somitogenesis forms somites, which give rise to muscles, bones, and connective tissue
• Morphogenesis shapes tissues and organs

Embryonic Period (Week 3-8)

• Critical period of development, during which major organs and body systems form
• High susceptibility to teratogens, which can cause birth defects

Fetal Period (Week 9-Birth)

• Growth and maturation of organs and body systems
• Development of sensory organs and neural connections

Embryonic Stem Cells

• Totipotent stem cells can give rise to all cells in the body
• Pluripotent stem cells can give rise to all cells in the body, except for extra-embryonic tissues
• Multipotent stem cells can give rise to multiple cell types within a specific lineage
• Adult stem cells are multipotent cells found in adult tissues, able to differentiate into specific cell types